It has been deemed desirable to illuminate a distant object with a light beam generated by a high energy laser (H.E.L.). The laser light beam is directed at a high energy light beam reflector and a particular wavelength component thereof reflects off of the reflector and is directed at the distant target. The reflected light energy from the illuminated target is redirected along the same path as the transmitted beam, and is separated by a light separator which redirects the reflected beam along a different optical axis than the optical axis of the light energy coming from the laser and striking the reflector. Such a prior art light separator is illustrated in FIG. 1 wherein the illuminating beam 1 from the high energy laser impinges upon the reflector surface 2, and a particular wavelength component is projected along path 3 toward the target. The reflected beam from the distant target transverses path 4 and impinges upon a sawtooth reflective structure 5 which is positioned beneath the reflective layer 2, and such reflected energy is redirected along path 6 to a detector system, not shown. The return beam, which has a different wavelength than the outgoing H.E.L. beam, is either a thermal beam or a return from an illuminator. Because the light separator of FIG. 1 is subjected to high temperature levels due to being impinged upon by the high energy laser light, heat exchanger 7 is positioned beneath the sawtooth reflective structure 5 to draw off the heat generated. Portion 8 of the light separator is typically formed of zinc selenide, and heat exchanger 7 comprises a copper or molybdenum block having fluid containing cooling pipes 9 buried therein, to draw the heat away from the light separator.
The reflective long period grating 5 shown in FIG. 1 is difficult to form and polish, and the formation of optically flat reflective sawtooth portions thereof has not been attainable. Thus it is highly desirable to produce a similar but superior device in a simpler and more inexpensive manner for performing these functions.